The VPLS (Virtual Private LAN Services) is the L2VPN technology based on the Internet Protocol (IP)/Multi Protocol Label Switching (MPLS) and the Ethernet technology, and it is able to provide multi-point services like Ethernet in the Metropolitan Area Network (MAN) and the Wide Area Network (WAN). It establishes and maintains a pseudo wire (PW) between the provider edge (PE) nodes, encapsulates the layer 2 protocol frame and transmits and switches it through the PW, so that multiple local area networks in the wide area domain are integrated into one network in the data link layer, to provide the users with the virtual Ethernet service, thus supporting the point-to-point, point-to-multipoint and multipoint-to-multipoint services, which can support carrier-grade Ethernet services in a relatively large network scale.
In the past, the VPLS network is mainly used for forwarding unicast messages, and currently, with the development of multicast technology, the VPLS network transmits not only the unicast messages but also the broadcast, multicast and/or unknown unicast messages. When transmitting the broadcast, multicast and/or unknown unicast messages, it needs to rely on the provider edge to replicate the broadcast, multicast and/or unknown unicast messages, and it sends them to each receiving custom edge (CE) through a number of pseudo wires. As shown in FIG. 1, if the aforementioned pseudo wires transmit the data through the same shared physical path, there might be multiple copies of the same broadcast, multicast and/or unknown unicast messages in the shared physical path, which wastes the network bandwidth.
Furthermore, the VPLS multicast technology is proposed by optimizing and improving the VPLS regarding to the multicast. The VPLS multicast technology provides the multicast service via the multicast tree of the operator. The VPLS multicast has the Inclusive Tree and the selective Tree, and the input source of the VPLS multicast is the IP multicast service data on the Attachment Circuit (AC) connected to the PE. The IP multicast service data generally use the inclusive tree to transmit, only when the IP multicast traffic exceeds the preset threshold value, the selective tree is used to transmit. As shown in FIG. 2, if the multicast tree of the operator is a inclusive tree aggregating multiple VPLS instances, that is, multiple services are transmitted through one multicast tree of operator, in order to distinguish the services at the user side, the IP multicast data need to be encapsulated with one VPLS instance label, and then it is transmitted via a point-to-multipoint (P2MP) multicast tree of the operator to the leaves on the P2MP multicast tree, that is the label switched router (LSR), of the operator.
Applying the aforementioned VPLS multicast optimization technology in the VPLS network needs to support the VPLS multicast signaling function; at the same time, the VPLS multicast uses the Border Gateway Protocol (BGP) as the signaling, which requires all the devices in the VPLS network to support the BGP protocol, since the complexity of the BGP protocol itself has relatively high requirements for the equipment, its implementation is relatively complicated, resulting in high operating cost.